Dynamoelectric machines, such as electric motors and generators, generally include hollow cylindrical stator cores which surround a rotatable rotor assembly. Electrical conductors are disposed in slots opening toward the hollow center of the stator core to react to or to generate electromagnetic fields. Generally, the conductors are coils of wire wrapped through the slots and around the ends of the slots in a winding pattern. In an electric motor, for example, energizing the coils generates an electromagnetic field in the core to rotate the rotatable rotor assembly in the hollow center. To generate the electromagnetic field and to prevent shorting, the core is electrically insulated from the coils of wire, and in a multi-phase machine, different phases of windings are insulated from one another at the end turn windings, the portion of the windings that extend from the ends of the slots in the stator core. Thus, end turn winding insulators, generally referred to as phase insulation, are generally used to insulate the different phases of windings from each other.
Phase insulation generally is formed of a rectangular piece of dielectric material formed into a ring. In a stator core having an inner set of windings and an outer set of windings, the windings are inserted into the slots of the stator core, and then the inner and the outer winding end turns are manually pried apart to insert the phase insulation therebetween. This is a very imprecise, slow and tedious process.
Various attempts have been made to automate the insertion process, but all have been unsatisfactory in several regards. One solution proposed inserting the outer set of windings, then inserting the phase insulation and then inserting the inner set of windings in three separate steps to effectively interpose the phase insulation between the inner and the outer sets of windings. This process, however, is still too slow and further improvements would be desirable. Furthermore, common problems with previous insertion techniques include tearing or misalignment of the phase insulation, which require manual adjustment and further inspection that offset any gains in efficiency from the automatic insertion process.
In addition, rectangular phase insulation which is formed into a cylinder cannot accommodate stator cores of different diameters. If the rectangular insulation is too short, there is a gap in the phase insulation. If the rectangular insulation is too long, the insulation tends to shift toward or away from the stator core as it folds. As a result, an excessive number of end windings are exposed and the chances for a short circuit greatly increase.
After the windings and insulation are put into a stator core, they are stitched or otherwise bound together to fix their relative positions. As the windings and insulation are stitched, the side of the insulation adjacent the stator core is pulled up against the underside of the windings. Occasionally some of the dielectric material extends under the windings and into the hollow center of the stator core where it can interfere with the rotation of the rotor.